1. Field of the Invention
The present invention relates to an optical device having one optical fiber or a plurality of optical fibers (optical fiber array) and a method of producing the same. In particular, the present invention relates to an optical device which is preferably used when a signal light, which is transmitted through an optical fiber, is monitored at an intermediate position of the optical fiber, and a method of producing the same.
2. Description of the Related Art
Nowadays, a wavelength division multiplexing by an optical fiber amplifier has been developed. A quantity of light transmitted through an optical fiber is monitored at respective wavelengths in the wavelength division multiplexing. After a quantity of light monitored is adjusted, a quantity of light adjusted is amplified by the optical fiber amplifier to maintain an amplifier's characteristics.
A variety of methods are known for the monitoring. However, monitor devices are mounted for respective fibers. Therefore, an optical device is larger in size.
For this reason, it is demanded to realize a small size and a high density of the monitor device. Further, when the monitoring is performed, a part of the signal light is split from the optical fiber. However, it is demanded to monitor a signal light transmitted through the optical fiber without attenuation of the signal light.
A technique as shown in FIG. 42 has been hitherto disclosed (for example, see Japanese Laid-Open Patent Publication No. 2001-264594). In this technique, an optical fiber 204 is disposed on a V-groove 202 formed on a glass substrate 200, and then a parallel groove 206 is formed in the glass substrate 200 so that the parallel groove 206 extends obliquely across the optical fiber 204 (with respect to the optical axis of the optical fiber 204). As shown in FIG. 44, a member 208 for reflecting light (optical member) is inserted into the parallel groove 206, and a gap of the parallel groove 206 is filled with an ultraviolet-curable resin (adhesive) 210.
Accordingly, as shown in FIG. 43, a signal light 212 transmitted through the optical fiber 204 is reflected by the member 208 and a light component (reflected light) 214 of the signal light 212 is split outside a clad of the optical fiber 204. Therefore, when the reflected light 214 is detected, for example, by a photodetector 216, it is possible to monitor the signal light 212.
The conventional art is also disclosed as shown in FIG. 45 (for example, see Japanese Laid-Open Patent Publication No. 2001-264594). In this art, a groove 200 is provided on the upper surface of a glass substrate 202, and an optical fiber 204 is placed and fixed in the groove 204 of the glass substrate 202. An end surface 206 (inclined end surface) is formed by cutting with a dicing saw. Further, a reflector 208 of a metal film is stuck with a resin to the inclined end surface 206. A light-receiving element 210 is provided on the upper surface of the glass substrate 202.
Accordingly, a light component 214 having a specified wavelength, which is included in a signal light 212 transmitted through the optical fiber 204, is reflected by the reflector 208, and the light component 214 is split to the outside of the clad. Therefore, when the reflected light 214 is detected with the light-receiving element 216 disposed on the glass substrate 202, it is possible to monitor the signal light.
In the case of the conventional monitor device as shown in FIG. 42, the member 208 is a distinct optical member from the glass substrate 200 and the optical fiber 204 and is inserted into the parallel groove 206 provided to the glass substrate 200 and the optical fiber 204. Therefore, at first, it is necessary to position the member 208 accurately. However, when the adhesive 210 is injected into the gap, the position of the member 208 in the parallel groove 206 is shifted by the adhesive 210 and it is difficult to position the member 208 in the parallel groove 206.
Further, it is necessary to decide the width of the parallel groove 206 so that the member 208 is inserted into the parallel groove 206 and the adhesive 210 is injected into the gap of the parallel groove 206. Therefore, it is difficult to realize an optical device having a relatively small size. Further, the signal light 212 transmitted through the optical fiber 204 is greatly attenuated at the parallel groove 206.
If the width of the parallel groove 206 becomes narrower, it is possible to realize an optical device having a small size and to restrain the attenuation of the signal light 212. In this case, it is necessary to narrow the width of the member 208. As a result, the mechanical strength of the member 208 is insufficient and the optical device cannot be used due to the a cycle and a handling during producing the optical device.
The parallel groove 206 is formed between the top surface of the glass substrate 200 and the bottom surface the glass substrate 200. Therefore, if the width of the parallel groove 206 becomes narrower, the machining load to the glass substrate 200 is increased during the cutting and the machining accuracy and the surface accuracy of the parallel groove 206 are decreased.
In the case of the conventional monitor device as shown in FIG. 45, the light-receiving element 210 is installed directly on the glass substrate 202. Therefore, the distance, which ranges from the clad surface of the optical fiber 204 to the upper surface of the glass substrate 202 (especially the surface on which the light-receiving element 210 is installed), is lengthened in some cases, and the reflected light 214, which comes from the reflector 208, comes into the light-receiving surface of the light-receiving element 210 in an oblique direction in other cases.
The spot diameter of the reflected light 214 is increased exponentially as the optical path of the reflected light 214 is lengthened. Therefore, the spot diameter of the reflected light 214 is possibly larger than the diameter of the light-receiving surface of the light-receiving element 210, for example, when the light-receiving element 210 is installed outside the clad with a refractive index-adjusting layer.
In another case, when the reflected light 214 comes obliquely with respect to the light-receiving surface, the spot diameter of the reflected light 214 may also be larger than the diameter of the light-receiving surface of the light-receiving element 210. In such a situation, a part of the spot of the reflected light 214 may protrude from the light-receiving surface, which may result in the loss of the reflected light 214, and the light-receiving sensitivity may be lowered. In the case of an optical fiber array in which a plurality of optical fibers 204 are arranged, the so-called crosstalk may be caused, in which the reflected light 214 of a certain optical fiber 204 comes into the light-receiving element 210 corresponding to an adjacent optical fiber 204.
In view of the above, in order to solve the problem as described above, the angle of the end surface 206 of the glass substrate 202, i.e., the angle with respect to the vertical plane may be increased to decrease the angle of incidence into the light-receiving surface of the light-receiving element 210. However, when it is assumed that another optical part is installed on the end surface 206 of the glass substrate 202, the angle of inclination of the end surface cannot be increased extremely for the optical part to be connected to the optical fiber 204 in relation to the strength and the demand for the miniaturization.
Therefore, if the angle of the end surface 206 of the glass substrate 202 is increased, it is difficult to fix another optical part to the end surface 206 of the glass substrate 202. Further, the distance, which ranges from the end surface of the optical fiber 204 to the other optical part, is lengthened, and the signal light may be greatly attenuated.
If the light-receiving element is installed closely to the end surface 206 on the upper surface of the glass substrate 202, the following problem may arise. When another optical part is installed on the end surface 206 of the glass substrate 202, for example, the end surface 206 of the glass substrate 202 and the other optical part may be fixed with a UV adhesive or UV-curable adhesive. In such a case, the ultraviolet light is radiated from a position over the end surface 206 of the glass substrate 202 toward the end surface 206. However, as described above, if the light-receiving element 210 is installed closely to the end surface 206, the light-receiving element 210 interposes in the path of radiation of the ultraviolet light. The ultraviolet light may not be radiated onto the UV-curable adhesive sufficiently, and it is impossible to cure the adhesive.
In the conventional monitor device as described above, another optical part (optical waveguide path) may be joined to an end surface of the optical fiber of the monitor device, for example, with an adhesive.
However, if the adhesive is used, exfoliation or deterioration of the adhesive may be caused due to changes over time thereof. For example, if any exfoliation of the adhesive is caused on the end surface of the optical fiber, the following situation is assumed. Even when an angle at which the reflected light is not returned to the core is adopted as the angle of inclination of the end surface of the optical fiber, the reflected light may be returned to the core depending on the condition of the exfoliation surface of the adhesive (for example, the shape and the angle of the surface of the adhesive).
In such a situation, if the reflected light is returned to the core of the optical fiber, the reflected light harmfully affects on the light source or the like.